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Abstract:People may be surprised to notice certain regularities that hold in existing knowledge they have had for some time. That is, they may learn without getting new factual information. We argue that this can be partly explained by computational complexity. We show that, given a knowledge base, finding a small set of variables that obtain a certain value of R2 is computationally hard, in the sense that this term is used in computer science. We discuss some of the implications of this result and of fact-free learning in general.

FiveThirtyEight covered the ongoing debate over teacher evaluation, citing two companion papers that appeared together in the September 2014 issue of the American Economic Review. In "Measuring the Impacts of Teachers" I and II the authors construct "value-added" estimates for teachers in a large urban school district by observing how students' test scores change from year to year as they pass through each teacher's classroom. They find that their teacher value-added scores are not significantly biased and are potent predictors of students' later-life outcomes.

Wonkblog covered an article published this month in the American Economic Journal: Applied Economics. In Saving Lives at Birth: The Impact of Home Births on Infant Outcomes the authors study a sample of over 300,000 Dutch women and find that home birth increases the risk of newborn mortality, especially for low-income women, likely because of reduced access to medical technologies after delivery.

A Wall Street Journalanalysis of potential merger activity in the health insurance industry cited a study published in the American Economic Review. In "Paying a Premium on Your Premium? Consolidation in the US Health Insurance Industry," the authors found that a 1999 merger between two large U.S. health insurers drove up customer premiums and depressed doctors' earnings in certain parts of the country.